Display device and method for manufacturing display device

The present disclosure relates to a display device such as a self-luminous display device including light emitters such as light-emitting diodes (LEDs), and a method for manufacturing the display device.

Known display devices are described in, for example, Patent Literatures 1 and 2.

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2017-009725

Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2015-194993

In an aspect of the present disclosure, a display device includes a substrate including a first surface, a side surface, and a second surface opposite to the first surface, a pixel unit located on the first surface and including a light emitter, a first connection pad adjacent to an edge on the first surface and electrically connected to the pixel unit, a second connection pad adjacent to the edge on the second surface, and a side wire extending from the first surface through the side surface to the second surface and connecting the first connection pad and the second connection pad. The first connection pad and the second connection pad have different sizes.

In another aspect of the present disclosure, a method for manufacturing a display device includes preparing a mother substrate including a first surface, a second surface opposite to the first surface, and a plurality of display device areas on the first surface, forming a plurality of pixel areas on each of the plurality of display device areas, forming a first connection pad on a portion adjacent to an edge on each of the plurality of display device areas, forming a second connection pad having a size different from a size of the first connection pad on a portion adjacent to the edge on the second surface, cutting the mother substrate along the edge of each of the plurality of display device areas to form display device substrates, and forming, on each of the display device substrates, a side wire extending from the first surface through a cut surface being a side surface to the second surface to connect the first connection pad and the second connection pad.

The structure that forms the basis of a display device according to one or more embodiments of the present disclosure will now be described. Patent Literature 1 describes a display device that includes pixel units each including self-luminous light emitters such as light-emitting diodes (LEDs) or organic electroluminescent elements. Patent Literature 2 describes a composite large display device (hereafter also referred to as a multi-display) including multiple tiled display devices.

Known display devices include, as wiring to drive a display, for example, wiring on the front surface of a substrate on which the display is located and wiring on the back surface of the substrate on which components such as a drive are located. Such display devices include a feedthrough conductor extending through the substrate from the front surface to the back surface and a connection conductor such as side wiring to connect a front connection pad connected to the wiring on the front surface and a back connection pad connected to the wiring on the back surface. The front and back connection pads in such display devices formed by, for example, photolithography may deviate from their intended positions by about several to several tens of micrometers due to, for example, misalignment of photomasks or the resolution limit based on the wavelength of a light source for exposure. Similarly, the connection conductor such as side wiring may also have positional deviations. Such positional deviations may increase difficulty in connecting the front connection pad and the back connection pad using the connection conductor. The connection between the front connection pad and the back connection pad may also deteriorate, increasing the resistance of the connection conductor. This may cause a lower manufacturing yield of display devices or uneven luminance or uneven colors in display images, and thus a lower image quality of display devices.

A display device according to one or more embodiments of the present disclosure will now be described with reference to the drawings. Each figure referred to below illustrates main components and other elements of the display device according to one or more embodiments of the present disclosure. The display device according to the embodiments of the present disclosure may thus include known components that are not illustrated, for example, circuit boards, wiring conductors, control ICs, and LSI circuits. Each figure referred to below is also schematic and is not drawn to scale relative to, for example, the actual positions and dimensional ratios of components of the display device.

is a schematic circuit diagram of a display device according to an embodiment of the present disclosure, illustrating circuit wiring and other components on a first surface of the display device.is a schematic circuit diagram of the display device according to the embodiment of the present disclosure, illustrating circuit wiring and other components on a second surface of the display device.is a partial plan view of the display device according to the embodiment of the present disclosure, illustrating its main part in an enlarged manner.is a cross-sectional view taken along line A-Ain.is a cross-sectional view taken along line A-Ain.is a cross-sectional view taken along line A-Ain.is a cross-sectional view of a display device according to another embodiment, corresponding to the cross-sectional view taken along line A-Ain.is a partial plan view of a display device according to a variation of the embodiment of the present disclosure, illustrating its main part in an enlarged manner.are development views of display devices according to two embodiments of the present disclosure, illustrating a side wire.is a cross-sectional view of a display device according to an embodiment of the present disclosure, illustrating a side wire. For simplicity,illustrates a pixel unit including light emitters and an electrode pad without illustrating other elements.each illustrate the display device without illustrating the side wire.each illustrate the display device without illustrating a part of the side wire (a part located on a side surfaceof a substrate).illustrate first to third surfaces on the same plane to clearly illustrate the side wire extending from the first surface through the third surface (side surface) to the second surface.

A display deviceincludes a substrate, a pixel unit, a first connection pad, a second connection pad, and a side wire.

The display deviceincludes the substrateincluding a first surface, a side surface, and a second surfaceopposite to the first surface, the pixel unitlocated on the first surfaceand including a light emitter, the first connection padlocated adjacent to an edgeon the first surfaceand electrically connected to the pixel unit, the second connection padlocated adjacent to the edgeon the second surface, and the side wireextending from the first surfacethrough the side surfaceto the second surfaceand connecting the first connection padand the second connection pad. The first connection padand the second connection padhave different sizes. The size of the first connection padmay also refer to the dimensions or the area of the first connection pad. The same applies to the size of the second connection pad.

The first connection padis electrically connected to the pixel unit. For example, the first connection padmay be connected to the pixel unitwith a thin-film transistor (TFT). More specifically, the first connection padmay be connected to the pixel unitwith an electrical intervening component such as a TFT, an electrode, or wiring.

The display devicewith the above structure produces the effects described below. When the first connection padand the second connection padhaving different sizes deviate from their intended positions due to lower printing accuracy or other causes, either the first connection pador the second connection padhaving a larger size can compensate for (accommodate) the positional deviation. This allows the first connection padand the second connection padto be appropriately connected to each other with the side wire, thus improving the manufacturing yield of the display deviceand the image quality. When the side wiredeviates from its intended position due to lower printing accuracy or other causes, the above effects also allow the first connection padand the second connection padto be appropriately connected to each other with the side wire.

For the size ratio between the first connection padand the second connection pad, or specifically the area ratio, the area of the larger pad may be, but not limited to, more than one time and not more than about five times the area of the smaller pad. However, with the value exceeding five times, the substratemay be too large.

The substrateis, for example, a transparent or opaque glass substrate, a plastic substrate, or a ceramic substrate. The substrateincludes the first surface, the second surfaceopposite to the first surface, and a third surfaceconnecting the first surfaceand the second surface. The first surfaceis also referred to as a display surface, and the second surfaceis also referred to as a non-display surface. The third surfaceis also referred to as a side surface or one side surface. The substratemay be a triangular plate, a rectangular plate, a hexagonal plate, a trapezoidal plate, a circular plate, an elliptic plate, or a plate with any other shape. The substratebeing, for example, an equilateral triangular plate, a rectangular plate, or an equilateral hexagonal plate facilitates tiling of multiple display devicesinto a multi-display. In the present embodiment, the substrateis a rectangular plate, as illustrated in, for example,.

The display devicemay include multiple pixel unitslocated on the first surface. The pixel unitsserve as a display area in the display device. As illustrated in, for example,, the pixel unitsare arranged in a matrix with a predetermined pixel pitch P. The pixel pitch P may be, for example, about 40 to 400 μm, about 40 to 120 μm, about 60 to 100 μm, or about 80 μm. A range of values referred to herein as one value to another value intends to mean the two values being inclusive.

Each pixel unitincludes an electrode pad(as illustrated in) and the light emitterelectrically connected to the electrode pad.

The light emitteris, for example, a self-luminous light emitter such as an LED, an organic electroluminescent element, or a semiconductor laser element. In the present embodiment, the light emitteris an LED. The light emittermay be a micro-LED. In this case, the light emitterconnected to the electrode padmay be rectangular as viewed in a plan view with each side having a length of about 1 to 100 μm inclusive, or about 3 to 10 μm inclusive.

The light emitteris electrically connected to the electrode padwith a conductive bond, such as a conductive adhesive, solder, or an anisotropic conductive film (ACF). The electrode padin the present embodiment includes an anode padand a cathode pad. The anode padis electrically connected to an anode terminalof the light emitter. The cathode padis electrically connected to a cathode terminalof the light emitter.

Each pixel unitmay include multiple anode pads, a single cathode pador multiple cathode pads, and multiple light emitters. The multiple anode padsare electrically connected with the multiple anode terminalsof the multiple light emitters. The single cathode pador the multiple cathode padsare electrically connected with the multiple cathode terminalsof the multiple light emitters. When the pixel unitincludes a single cathode pad, the cathode padcan be common to the multiple light emitters. The light emittersmay include a light emitterR that emits red light, a light emitterG that emits green light, and a light emitterB that emits blue light. In this case, each pixel unitenables display of color tones. Each pixel unitmay include, instead of the light emitterR that emits red light, a light emitter that emits orange, red-orange, red-violet, or violet light. Each pixel unitmay include, instead of the light emitterG that emits green light, a light emitter that emits yellow-green light.

As illustrated in, the structure may include a drive such as a power supply circuiton the second surface. The power supply circuitgenerates power supply voltages to be provided to the pixel units. The power supply voltages include a first power supply voltage VDD and a second power supply voltage VSS. The power supply circuitincludes a VDD terminalfor outputting the first power supply voltage VDD and a VSS terminalfor outputting the second power supply voltage VSS. The first power supply voltage VDD is an anode voltage of, for example, about 3 to 15 V or about 10 to 15 V. The second power supply voltage VSS is lower than the first power supply voltage VDD and is a cathode voltage of, for example, about −3 to 3V or about 0 to 3 V.

The power supply circuitmay include a control element such as a control circuit or an IC for controlling, for example, the emission or non-emission state and the light intensity of the light emitters. The power supply circuitmay be, for example, a thin film circuit on the second surface. In this case, the thin film circuit may include, for example, a semiconductor layer including low-temperature polycrystalline silicon (LTPS) formed directly on the second surfaceby a thin film formation method such as chemical vapor deposition (CVD).

The display devicemay include multiple first connection padslocated adjacent to the edgeof the substrateon the first surface. The first connection padsmay be at positions that are about 10 to 500 μm away from the edgeof the substrateon the first surfacetoward the center of the first surface. Each first connection padmay be at a distance of about half the pixel pitch P from the edgeof the substrate. In this case, multiple display devicescan be joined to be a multi-display with a pixel pitch between the display devicesequal to the pixel pitch for the display in each display device. This allows the multi-display to have a uniform pixel pitch and an improved image quality. For a multi-display being formed with light absorbers placed between adjacent display devices, for example, each first connection padmay at a distance shorter than half the pixel pitch P from the edgeof the substrate.

In the present embodiment, as illustrated in, the first connection padsmay include multiple first power supply connection padsand multiple second power supply connection pads. The first power supply connection padsare used to apply the first power supply voltage VDD to the pixel units. The second power supply connection padsare used to apply the second power supply voltage VS S to the pixel units.

The display deviceincludes a first wiring patternand a second wiring pattern. The first wiring patternand the second wiring patternare located on the first surface. The first wiring patternand the second wiring patterninclude layers of, for example, Mo/Al/Mo or MoNd/AlNd/MoNd. The stack of Mo/Al/Mo includes a Mo layer, an Al layer, and a Mo layer in this order. The same applies to other notations. MoNd is an alloy of Mo and Nd. As illustrated in, for example,, the first wiring patternelectrically connects the pixel unitsand the first power supply connection pads, and the second wiring patternelectrically connects the pixel unitsand the second power supply connection pads. The first wiring patternand the second wiring patternmay be planar and electrically insulated from each other with insulating layers (insulating layersanddescribed later) between them. The second wiring patternmay include the cathode padsof the electrode padsas parts of the second wiring pattern.

The display devicemay include multiple second connection padslocated adjacent to the edgeon the second surfaceat positions substantially corresponding to the first connection padsas viewed in a plan view. As illustrated in, the second connection padsmay include multiple third power supply connection padsand multiple fourth power supply connection pads. The third power supply connection padsare used to apply the first power supply voltage VDD to the pixel units. The fourth power supply connection padsare used to apply the second power supply voltage VSS to the pixel units.

The display devicemay include as many first power supply connection padsas the third power supply connection pads, and as many second power supply connection padsas the fourth power supply connection pads. Each first power supply connection padmay at least partially overlap one or more of the third power supply connection padsas viewed in a plan view. Each second power supply connection padmay at least partially overlap one or more of the fourth power supply connection padsas viewed in a plan view.

The first connection padsmay include connection pads connected to, for example, a scanning signal line (gate signal line), an image signal line (source signal line), or an emission control signal line. The same applies to the second connection pads.

As illustrated in, the display devicemay include a third wiring pattern. The third wiring patternis located on the second surface. The third wiring patternincludes layers of, for example, Mo/A/Mo or MoNd/AlNd/MoNd. The third wiring patternmay be thick film wiring including a conductive paste containing conductive particles of, for example, silver applied by, for example, printing, and fired. The third wiring pattern, for example, connects the VDD terminalin the power supply circuitand the third power supply connection pads, and connects the VS S terminalin the power supply circuitand the fourth power supply connection pads.

The display deviceincludes the side wireextending from the first surfacethrough the side surfaceconnecting the first surfaceand the second surfaceto the second surface. The display devicemay include multiple side wires. The side wiresconnect the first connection padsand the second connection pads. In the present embodiment, the side wireselectrically connect the first power supply connection padsand the third power supply connection pads, and electrically connect the second power supply connection padsand the fourth power supply connection pads. Some of the first connection padsand some of the second connection padsmay be connected to each other with feedthrough conductors located at the periphery of the substrateand extending through the substratefrom the first surfaceto the second surface. The first connection padsand the second connection padsare connected with the side wiresto easily reduce the area of the display deviceoutside the display area (specifically, a frame portion).

The pixel units, the first connection pads, the second connection pads, and the side wireswill now be described in detail with reference to.illustrate, among the multiple first connection pads, the multiple second connection pads, and the multiple side wires, a first connection pad, a second connection pad, and a side wirein the display deviceaccording to one embodiment.

As illustrated in, for example,, each pixel unitin the present embodiment includes the electrode padincluding three anode padsand one common cathode pad. Each pixel unitincludes the light emitterR that emits red light, the light emitterG that emits green light, and the light emitterB that emits blue light. The light emittersR,G, andB may be arranged in line as viewed in a plan view as illustrated in, for example,. The light emittersR,G, andB may be arranged in an L shape as viewed in a plan view. This allows each pixel unitto be smaller as viewed in a plan view, and to be compact and square as viewed in a plan view. The display devicethus includes pixels with higher density, allowing high-quality image display.

As illustrated in, for example,, each pixel unitincludes insulating layerstolocated on the first surfaceof the substrate. The insulating layerstoare inorganic insulating layers of, for example, SiOor SiNor organic insulating layers of, for example, an acrylic resin or polycarbonate. Although not illustrated, a pixel circuit including a TFT or another element for controlling the light emission of the light emitteris located inside the insulating layernearest the substrateof the insulating layerstoor between the insulating layerand the substrate. The insulating layersandare located between the first wiring patternand the second wiring patternand electrically insulating them from each other.

The light emitterincludes the anode terminalelectrically connected to the anode pad, and the cathode terminalelectrically connected to the cathode padthat is connected to the second wiring pattern. The anode padand the cathode padare electrically insulated from each other by an opening (cutout) around the anode padin the second wiring pattern. The cathode padis electrically connected to the second wiring patternwith wiring routed along the surfaces of the insulating layerand the inner wall of the opening in the insulating layer. The anode padand the cathode padmay have their surfaces coated with a transparent conductive layerof, for example, indium tin oxide (ITO) or indium zinc oxide (IZO).

The first connection padand the second connection padare made of a conductive material. The first connection padand the second connection padmay each include a single metal layer, or multiple metal layers stacked on one another. The first connection padand the second connection padinclude layers of, for example, Al, Al/Ti, Ti/Al/Ti, Mo, Mo/Al/Mo, MoNd/AlNd/MoNd, Cu, Cr, Ni, or Ag. In the example of, the first connection padincludes two metal layersandstacked on each other and located on an insulating layeron the first surfaceof the substrate. In the example of, the second connection padincludes a single metal layerlocated on the second surfaceof the substrate.illustrates a protective insulating layer (overcoat).

As illustrated in, for example,, the first connection padincluding the metal layersandstacked on each other may include an insulating layerbetween the edges of the metal layersand. The first connection padmay include an insulating layerat its inward (right in) end on the first surface. This reduces the likelihood of short-circuiting between the first connection padand a wiring conductor or another element located inward on the first surface. The insulating layers,, andare made of, for example, SiO, SiN, or a polymeric material such as an acrylic resin. The first connection padmay have its surface coated with a transparent conductive layerof, for example, ITO or IZO. The second connection padmay have its surface coated with a transparent conductive layerof, for example, ITO or IZO. The first connection padsother than the first connection padmay have the same or similar structure as the first connection pad. The second connection padsother than the second connection padmay have the same or similar structure as the second connection pad

As illustrated in, for example,, the side wireextends from the side surfaceto the first surfaceand to the second surface, and connects the first connection padand the second connection pad. The side wiremay include a conductive paste containing conductive particles of, for example, Ag, Cu, Al, or stainless steel, an uncured resin component, an alcohol solvent, and water. The conductive paste may be applied to an intended portion from the side surfaceto the first surfaceand to the second surfaceand cured by heating, photocuring using ultraviolet ray irradiation, or a combination of photocuring and heating. The side wiremay also be formed with a thin film formation method such as plating, vapor deposition, or CVD. The side surfacemay include a groove formed in advance to receive the side wire. This allows the conductive paste for the side wireto be easily received in the intended portion on the side surface. The side wiresother than the side wiremay be formed with the same or similar method to the side wire

Although not illustrated, the display deviceincludes multiple gate signal lines and multiple source signal lines intersecting with the gate signal lines on the first surface. Each pixel unitincludes multiple first electrode pads connected to the gate signal lines, multiple second electrode pads connected to the source signal lines, and a TFT for driving the light emitter connected to the first electrode pads and the second electrode pads. Although not illustrated, the display deviceincludes, on the second surface, multiple third electrode pads electrically connected to the first electrode pads, and multiple fourth electrode pads electrically connected to the second electrode pads. The first electrode pads and the third electrode pads may be connected to each other with, for example, side wires having the same or similar structure to the side wiresor. The second electrode pads and the fourth electrode pads may be connected to each other with, for example, side wires having the same or similar structure to the side wiresor. The third electrode pads may be connected to a gate signal line drive (gate driver) located on the second surfacewith, for example, back wiring. The fourth electrode pads may be connected to a source signal line drive (source driver) located on the second surfacewith, for example, back wiring. The gate signal line drive and the source signal line drive may be included in the power supply circuit.

As illustrated in, for example,, the display deviceincludes the first connection padand the second connection padhaving different sizes as viewed in a plan view. When the first connection padand the second connection paddeviate from their intended positions, either the first connection pador the second connection padhaving a larger size can compensate for the positional deviation. More specifically, as viewed in a plan view, either the first connection pador the second connection padhaving a larger size overlaps most of the smaller pad or includes the smaller pad. This allows the first connection padand the second connection padto be appropriately connected to each other with the side wire. When the side wiredeviates from its intended position due to lower printing accuracy or other causes, the above effects also allow the first connection padand the second connection padto be appropriately connected to each other with the side wire

Upon forming the side wirethat connects the first connection padand the second connection pad, a pattern for applying the conductive paste for the side wireis set based on, for example, the position of either the first connection pador the second connection padshaving a smaller area as viewed in a plan view. The side wirein such an application pattern allows the first connection padand the second connection padto be appropriately connected to each other. In other words, the display deviceallows greater positional deviations between the first connection padand the second connection padthan when the first connection padand the second connection padhave the same shape (specifically, the same area) as viewed in a plan view. The display devicemay also allow a positional deviation of the side wire. The display devicethus improves the manufacturing yield. The display devicealso allows multiple first connection padsand multiple second connection padsto be appropriately connected to each other, supplying a uniform and stable power supply voltage to the pixel units. More specifically, the pixel unitsreceiving input of the same power supply voltage are less likely to receive power supply voltages with different voltage levels. This can reduce uneven luminance or uneven colors in the display deviceand improve the image quality of the display device.

The second connection padmay be, as illustrated in, larger than the first connection padconnected to the second connection padas viewed in a plan view. For example, the second connection padmay have a larger area than the first connection pad. In this case, the area of the first connection padas viewed in a plan view can be small, reducing the frame portion of the display deviceand allowing the display deviceto have a smaller frame portion or no frame portion. This structure also facilitates arrangement of multiple first connection padsat positions corresponding to a small pixel pitch in the display devicethat displays high-definition images. With this structure, the display device, which allows positional deviation of the first connection padand the second connection pad, can include a smaller frame portion or no frame portion, and have a small pixel pitch. The structure can thus improve the manufacturing yield and the image quality of the display device. The structure also allows a multi-display including multiple display devicesto have a uniform pixel pitch and an improved image quality.

The second connection padmay be longer than the first connection padin the direction along the edge. This allows positional deviations of the first connection padand the second connection padin the direction along the edge. More specifically, for any positional deviation, the second connection padcan remain including the first connection pador overlapping most of the first connection padin the direction along the edge. This reduces the likelihood of deteriorating connection between the first connection padand the second connection padwith the side wire. The second connection padmay have, in the direction along the edge, a length of, but not limited to, more than one time and not more than about twice the length of the first connection padin the direction along the edge

The second connection padmay have a width (e.g., referred to as a width w) in a portion adjacent to and along the edgegreater than the width (e.g., referred to as a width w) in a portion along the edgeopposite to the portion adjacent to the edge. For example, as illustrated in, the second connection padmay have an extensionextending in the direction along the edgein its portion adjacent to the edge. This structure allows greater positional deviations between the first connection padand the second connection padin the direction along the edge. This also further reduces the likelihood of deteriorating connection between the first connection padand the second connection padwith the side wire. The extensionserves as a guide to draw the conductive paste in the depth direction (opposite to the edge) when the conductive paste is applied to form the side wire. This further improves the connection of the side wirewith the second connection pad. The second connection padmay have extensionsextending in the direction along the edgeat the two ends adjacent to the edge. This structure allows the above effects to be produced more effectively. To produce the same effects, the second connection padmay be trapezoidal with its side adjacent to the edgebeing the lower base and with its side opposite to the edgebeing the upper base. The width wmay be, but not limited to, more than one time but not more than about 1.5 times the width w. The first connection padmay also have a width in a portion adjacent to and along the edgegreater than the width in a portion along the edgeopposite to the portion adjacent to the edge

The second connection pad, as illustrated in, may have an extensionextending in the direction along the edgein a portion adjacent to the edge. The extensionmay have a width gradually decreasing from the end adjacent to the edgein the depth direction. In this case, the extensionserves more effectively as a guide to draw the conductive paste in the depth direction. The first connection padmay have the same or similar structure.

As illustrated in, for example,, the first connection padmay be located between the two ends of the second connection padin the direction along the edgeas viewed in a plan view. More specifically, the second connection padmay include the first connection padin the direction along the edge. In this case, the first connection padand the second connection padcan be connected to each other appropriately by setting a pattern for applying the conductive paste for the side wirebased on the position of the first connection pad. This can improve the manufacturing yield and the image quality of the display device, and thus the image quality of a multi-display.

The second connection pad, as illustrated in, may be longer than the first connection padin the direction intersecting with the direction along the edge. For example, as viewed in a plan view, the second connection padmay be longer than the first connection padin the direction orthogonal to the edge. This can increase the contact area between the second connection padand the side wireand can thus reduce the contact resistance between the second connection padand the side wire. This allows stable supply of a power supply voltage to the pixel units, thus further improving the image quality of the display device. The above intersecting direction may not be orthogonal to the edge, but may be inclined to the direction along the edgeat an angle. The angle may be about 30 to 80° or 60 to 80°.

The second connection padmay include the first connection padas viewed in a plan view. More specifically, the second connection padmay include the full portion of the first connection padas viewed in a plan view. This structure allows positional deviations of the first connection padand the second connection padin any direction. More specifically, for any positional deviation, the second connection padcan remain including the first connection pador overlapping most of the first connection padin any direction. When the side wiredeviates from its intended position due to lower printing accuracy or other causes, the above effects also allow the first connection padand the second connection padto be appropriately connected to each other with the side wire

Either the first connection pador the second connection padhaving a larger size may be circular or oval. This structure allows greater positional deviations between the first connection padand the second connection padin any direction. The second connection padin this structure may include the first connection padas viewed in a plan view. This structure allows still greater positional deviations between the first connection padand the second connection padin any direction.

The second connection padmay have a shape similar to the shape of the first connection pad. This structure allows greater positional deviations between the first connection padand the second connection padin any direction. The second connection padin this structure may include the first connection padas viewed in a plan view. This structure allows still greater positional deviations between the first connection padand the second connection padin any direction.